2DOF harness tensionner with Fly PTmover

[RacingMat]

Hi!

My cockpit is static, I've build a pressure gSeat with bladders and RC servo.
I wanted to increase immersion by a harness tensionner.

I'd already tested a static harness tensionner on a 2 DOF plateform, and the feeling was great.
As my rig is static, I'll have to actuate the harness but the advantage is that I can make a 2 DOF tensionner.

principle:
2 DOF harness -> the strength on the right shoulder and left shoulder will be different

both will react along Surge (longitudinal acceleration)
and Sway (lateral acceleration) will tight one shoulder or the other (depending on left turn or right turn)
(maybe later add some heave information?)

harness : 5 points
the 5th will prevent the harness to move up, this will give actual tension (vs movement)!

prefer larger harness 3" (vs only 2")

actuators:
RC servos 35kg.cm (5V to 8,3V)
PSU @7,3V

arduino:
code for 4 servos as I want to combine the harness and the gSeat pressure bladders also RC servo driven.

software:
FlyPT mover https://www.xsimulator.net/community/faq/flypt-mover.29/category

Here is a video showing step by step how I drive the 2 DOF belt with Fly PTmover:

The strength from 35kg.cm servo is enough.
Power up the servo, sit down, thight the belt as you wish, and start the sim. If you tight the belt before powering up the servos, they are loose and they could be pushed out of their range...

The only drawback, in my opinion is the noise of the servos: they are whinning...

here some infos gathered in this FAQ https://www.xsimulator.net/community/faq/harness-tensioner-simulation.361/

► shopping list
"HV high torque servo motor Robot servo 35kg RDS3235 Metal gear Coreless motor digital servo arduino servo for Robotic DIY"

1X HV hohe drehmoment servo motor Roboter servo 35kg RDS3235 Metall getriebe Kernlosen motor digital servo arduino servo für robotic DIY - AliExpress 26

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

17€
I chose 270° range
You'll need a dedicated power supply (5V slower to 7,4V fastest)

Speed: 0.13sec/60 degree at(5v)
0.12sec/60 degree at(6v)
0.11sec/60 degree at(7.4v)

Torque: 29kg.cm.at(5v) -1.9A
32kg.cm.at(6v) -2.1A
35kg.cm.at(7.4v) -2.3A

or stronger but unecessary in my opinion
60kgcm 24€
https://www.aliexpress.com/item/4000055027119.html

speed is voltage related
torque is current related!

1/ choose speed AKA voltage
2/ check the spec which gives you the current at chosen voltage
3/ buy your PSU ;-)

if you choose 7,4V PSU, verify it'll be able to deliver up to 2.3A in order to give full torque (add a BIG margin ;-) )
https://fr.aliexpress.com/item/32823922664.html
11€ 7V 10A


here is my ball bearing support (12€ for 2 supports)
they are made of:
P000 https://www.aliexpress.com/item/32833812473.html
Zinc Alloy Diameter Bore Ball Bearing Pillow Block Mounted Support
they allow a big static disalignment as the bearing is mounted like a joint articulation

and 200mm Ø10 linear shaft Cylinder Chrome Plated Liner Rods
https://www.aliexpress.com/item/4001294745058.html

► budget:
2x 17€ for 35 kg.cm servo
11€ for 7V 10A PSU
(maybe consider a 12V 10A PSU + an Adjustable Power Module Constant Current 5A)
12€ for bearing rollers
15€ any arduino with a USB port (an original to support the community or a clone)

50€ for a used 3" width 5 points harness
total = 120€ all included



arduino code (for up to 4 servos)

// Multi Direct
// -> 4 servos
// <255><LeftBelt><127><127><RightBelt>
// Rig : Bit output -> 8 bits
// avec inversion
// PT Mover envoie de 0 à 255 par axe

/*Mover = output "Binary" et "10bits"
Arduino = Byte Data[2]
Data[0] = Serial.read();
Data[1] = Serial.read();
result = (Data[0] * 256 + Data[1]);

OU

Mover = output "Binary" et "8bits"
Arduino = Byte Data
Data = Serial.read(); on obtient directement le résultat*/

#include <Servo.h>  // local library "Servo.h" vs library partagée <Servo.h>

const byte nbServos = 4;

// create servo objects to control any servo
Servo myServo[nbServos];
const byte servoPin[nbServos] = {2, 3, 4, 5};  // pins digitales (pas forcément ~pwm)
const byte inversion[nbServos] = {1, 1, 0, 0 }; // paramètre à changer si un servo part le mauvais sens
int OldSerialValue[nbServos] = {0, 0, 0, 0};
int NewSerialValue[nbServos] = {0, 0, 0, 0};

// servo span:
int servoHomeDegres[nbServos] = { 0, 0, 0, 0}; //sera mis à jour avec la mesure de pression initiale
int servoMaxDegres[nbServos] = { 90, 90, 90, 90}; // cuisseG, cuisseD, côtéG, côtéD
int servoPositionTarget[nbServos] = {0, 0, 0, 0};

const byte deadZone = 0;

// =======================================
// Variables for info received from serial
// =======================================
int bufferPrevious = 0;      // To hold previous read fom serial command
int bufferCurrent = 0;       // To hold current read fom serial command
int bufferCount = 0;         // To hold current position in bufferCommand array
// byte bufferCommand[2*nbServos] = {0};  // (*2 if 10 bits) To hold received info from serial
int bufferCommand[4] = {0};  // To hold received info from serial

void setup()
{
  Serial.begin(115200); // opens serial port at specified baud rate

  // attach the Servos to the pins
  for (byte i = 0; i < nbServos; i++) {
    // pinMode(servoPin[i], OUTPUT); // done within the library
    myServo[i].attach(servoPin[i]);  // attaches the servo on servoPin pin
    }
  // move the servos to signal startup
  MoveAllServos255toDegres(125); // mi-course
  delay(1000);
  // send all servos to home
  MoveAllServos255toDegres(0);
}

void loop()
{
  // SerialValues contain the last order received (if there is no newer received, the last is kept)

  if (Serial.available())
  {
    bufferPrevious = bufferCurrent; // Store previous byte
    bufferCurrent = Serial.read(); // Get the new byte
    bufferCommand[bufferCount] = bufferCurrent; // Put the new byte in the array
    bufferCount++; // Change to next position in the array
    if (bufferCurrent == 255) bufferCount = 0; // one 255 is the start of the position info
    if (bufferCount == nbServos) //si 8 bits, nbServos // si 10 bits nbServos*2
      //Having reach buffer count, means we have the new positions and that we can update the aimed position
    {
      for (byte i = 0; i < nbServos; i++) {
        NewSerialValue[i] = bufferCommand[i];
        //NewSerialValue[i]= (bufferCommand[i*2] * 256) + bufferCommand[i*2+1]; // si 10 bits
      }
      bufferCount = 0;
    }
  }
  // Update orders sent to motor driver
  for (byte i = 0; i < nbServos; i++) {
    if (abs(OldSerialValue[i] - NewSerialValue[i]) > deadZone) {
      if (inversion[i] == 1)
      {
        envoiServoConsigne255toDegres(i, (255 - NewSerialValue[i]));
      }
      else
      {
        envoiServoConsigne255toDegres(i, NewSerialValue[i]);
      }
      OldSerialValue[i] = NewSerialValue[i];
    }
  }
}

void envoiServoConsigne255toDegres(byte servoID, int val )
{
  byte targetDegres;
  val = constrain(val, 0, 255); // constrain coupe au dessus et en dessous : écrêtage et pas mise à l'échelle (comme map)
  // sécurité pour éviter les cas où Simtools enverrait du négatif ou au-delà de 255
  targetDegres = map(val, 0, 255, servoHomeDegres[servoID], servoMaxDegres[servoID]);
  //  map(value, fromLow, fromHigh, toLow, toHigh)
  myServo[servoID].write(targetDegres);              // tell servo to go to position in variable : in steps of 1 degree
  // servo.write(angle)  -> angle: the value to write to the servo, from 0 to 180
}

void MoveAllServos255toDegres( int target)
{
  // send all servos to home
  for (byte i = 0; i < nbServos; i++) {
    envoiServoConsigne255toDegres(i, target);
  }
}

here is the setup:

and the file itself: replace .txt extension by .Mover extension

 

[blekenbleu]

Any other thought

I have not used SimHubDash. While some SimHub code is available, much is not.
Thus , one has to guess/choose whether, as closed source "other" code evolves
(potentially impacting API and ABI), how much "own" code one is prepared to rewrite.

Your seat motion presumably depends on the same telemetry used for belt tensioning,
for which my code was hacked before @Wotever released his.
Consider repurposing his harness tensioning Arduino code, available by his discord.

Only some of the times the motor moves when i use this method

Engineering and problem solving both involve breaking things down into simpler pieces.
I write a lot of code for unit testing that does not make it into released code,
and a lot of Arduino code to report diagnostics back over serial for tracing what is or is not happening, with considerable committing changes to GitHub, so that versions can be reverted when appropriate. Learning largely involves mistakes.
Using SimHub's Custom Serial interface allows exercising the full range of values to be handled by Arduino code in a controlled manner.

 

[dadima]

Consider repurposing his harness tensioning Arduino code, available by his discord

I did look for the code for his version however due to my lack knowledge on the programming and the complicated code that he is using, I believe it is quite impossible for me to use it with normal dc motor equipped with just pot on the shaft attached.

Using SimHub's Custom Serial interface allows exercising the full range of values to be handled by Arduino code in a controlled manner.
Indeed, the custom serial device open a lot of potential possibilities for the usage and testing. As for now, I'll stick with my SHCustomProtocol.h editing as I were able to understand a bit about their ncalc, and was able to make my motor respond according to it's serial output based on the basic ncalc formula given.
Thanks for such inspiration that you made. Yours version of the tensioner that were released before the developer's version really make the racing sim to the next level.

 

[blekenbleu]

impossible for me to use it with normal dc motor equipped with just pot on the shaft attached.

Oops, an essential aspect of using PWM with DC motor for harness tension is that no shaft potentiometer is required.

PWM directly controls DC motor torque, which directly controls harness tension with no need for any servo feedback control.

 

[dadima]

Oops, an essential aspect of using PWM with DC motor for harness tension is that no shaft potentiometer is required.

PWM directly controls DC motor torque, which directly controls harness tension with no need for any servo feedback control.

Well, I might need to look further more into your code to get mine working without the pot attached. Just curious about how the pwm will determine the center, max and low limit of let say, my lever attached to the motor shaft.
Thanks for replies

 

[blekenbleu]

how the pwm will determine the center, max and low limit
of let say, my lever attached to the motor shaft.

Affordable direct drive DC motors lack torque to use levers. Instead, motor shafts become axles around which rapidly winds e.g. wire or fishline attached to the harness.
Angular position does not matter; sort of like fishing reel drag,
motors quickly wind until stalled at torque allowed by driving PWM,
releasing as quickly when PWM duty cycle decreases.

As a contrary example, consider a motor shaft long (2-3 inches) enough to wrap harness webbing width. Effectively increasing radius of winding web layers would stall motors at much reduced tension.

 

[blekenbleu]

Affordable direct drive DC motors lack torque to use levers

@Bridle, on SimHub discord, reports success using hoverboard wheels to tension belts
e.g. US$45 used https://www.ebay.com/itm/234763413161

 

[RacingMat]

Yes, hoverboard is typically a torque driven motor and would be highly suitable for a belt tensioner.
But is the driver included with the 2 hoverboard motors @45$? Or is it to be purchased separately?

 

[blekenbleu]

is the driver included with the 2 hoverboard motors

Probably not. Hoverboard Motor Characterization
Controlling a Hoverboard Motor with a Simple Arduino
US$15 on eBay https://www.ebay.com/itm/174511216561
US$17 on Amazon https://www.amazon.com/dp/B087M2378D

 

[blekenbleu]

Hmm, researching a bit more, it seems that unmodified hoverboard motors are poor at controlling torque while stalled, needing much higher than 3 phase resolution:

Very little torque at low RPM, stalling motors​

​

https://discourse.odriverobotics.com/t/how-are-motor-currents-given/5280​

https://discourse.odriverobotics.com/t/10-nm-torque-motor-selection/5636

 

[blekenbleu]

Powered from a 12V auto battery

Good nominal 24V scooter motor response from 12V auto battery benefits from high peak current capability, which typically wants supercapacitors when not using a battery.
This Car Battery Jump Starter bundles peak current goodness in a preassembled unit, and is among the cheapest including an AC charger and 12VDC accessory port.
One potential drawback is slow recharging rate (15W), but that limitation seems typical even among much more expensive alternatives.

 

[blekenbleu]

Kicking off some scooter motor PWM control testing...